The present invention relates to an assembly and a device for optical beam transformation, in particular an assembly, which is useful for imaging a light source or several light sources onto the front face of an optical fiber, comprising at least one light source that is capable of emitting at least one beam of light and further comprising one imaging element and at least one device for optical beam transformation, the imaging element being able to image the at least one beam of light emitted from the at least one light source onto the at least one device for optical beam transformation, through which the at least one beam of light can at least partially pass, the at least one device for optical beam transformation being able to rotate the beam of light passing through said device at least in sections about the direction of propagation of the respective section of the beam or beams of light by an angle of about 90xc2x0.
An assembly and a device of the aforementioned type are known from the European Patent Specification EP 0 484 276 B1. In the assembly described therein the light from several diode lasers arranged in a row is focussed onto the front face of an optical fiber. Instead of several diode lasers the light from a laser diode bar with several linear light-emitting sections arranged in a row may also be imaged onto the front face of the optical fiber. In the mentioned patent specification one Abbxc3xa9-Kxc3x6nig-prism per partial beam of one of the diode lasers serves as device for optical beam transformation. Each of these beams of light, having an essentially linear cross-section, is rotated in each of these Abbxc3xa9-Kxc3x6nig-prisms by approximately 90xc2x0. Such a rotation of beams of light originating from linear light sources arranged in a row has been found to be useful, especially because an effective imaging of the individual partial beams upon the front face of the optical fiber with simple means may be rendered impossible because of interpenetration of the individual partial beams due to divergence of the individual partial beams in the direction of the longitudinal extension of the light source. The use of an Abbxc3xa9-Kxc3x6nig prism to rotate the individual partial beams turns out to be disadvantageous however, because for one thing the Abbxc3xa9-Kxc3x6nig prism is an expensive optical component with a very complex design. For another, the individual partial beams must be fed separated from each other into a considerable number of adjacent separate Abbxc3xa9-Kxc3x6nig prisms. Due to the required separation into individual partial beams or bundles of partial beams the light from a two-dimensionally extended light source cannot be effectively imaged into a given section of space and in particular cannot or can only far from completely be rotated in segments or sections with the previously known device.
The object of the present invention is the creation of an assembly for optical beam transformation of the initially mentioned kind and a device for optical beam transformation of the initially mentioned kind which are simpler and cheaper to manufacture and can be used more effectively.
According to the invention this is achieved by an assembly with the elements of and a device with the elements of. According to the invention the at least one entry plane and/or the at least one exit plane of the device for optical beam transformation comprises at least one segment of cylindrical lens. With such a device, light emitted from light sources in the form of a point, of groups of points, or from linear or two-dimensionally extended light sources can be rotated, in particular rotated in segments.
In one embodiment of the assembly according to the invention the cylinder axis of the at least one segment of cylindrical lens may be inclined within the plane of the entry and/or exit plane with respect to the longitudinal direction of the substantially linear or rectangular cross-section of an incident beam of light, preferably by an angle of about 45xc2x0. In particular, at an inclination of the cylinder axis of about 45xc2x0 the incident beam of light is rotated by about 90xc2x0 in its entirety or in segments. The at least one entry and/or exit plane may have a substantially elongated, preferably a rectangular form, in which case the cylinder axis of the at least one segment of cylindrical lens will be inclined within this plane by an angle of preferably 45xc2x0 with respect to the longitudinal direction of the plane.
It is advantageous for both the at least one entry plane and the at least one exit plane to comprise segments of cylindrical lens that are arranged facing each other in the central direction of propagation of the beams of light that are incident upon the device. Preferably the at least one entry plane and the at least one exit plane each comprise a number of segments of cylindrical lens of identical focal length that are arranged next to each other and in parallel to each other. This arrangement ensures that beams of light emitted by a two-dimensionally extended light source enter the device through segments of cylindrical lens arranged next to each other and exit through the facing segments of cylindrical lens, with all partial beams passing through the device being rotated or deflected, respectively, in an analogous way because of the identical focal length of all segments of cylindrical lens.
According to an alternative preferred embodiment the at least one entry plane and/or the at least one exit plane are provided with a number of segments of cylindrical lens, advantageously having identical focal lengths, which are arranged next to each other, with adjacent segments being at an angle, preferably a right angle, to each other. When the light from a two-dimensionally extended light source falls upon two adjacent segments of cylindrical lens that are oriented at right angles to each other, the respective sections of the beam of light incident upon these segments are rotated by +90xc2x0 and xe2x88x9290xc2x0, respectively, in passing through the device. By choosing the point of rotation in an advantageous way, the sections of the beam of light incident upon adjacent segments of cylindrical lens that are oriented at right angles to each other are folded towards each other in such a way that after passing through the device the distance between them is reduced to zero. As a particular result the extension of the two-dimensionally extended incident beam of light is halved in one direction and doubled in the other direction. Particularly in the case of light sources that are more extended in the one than in the other direction this amounts to a balancing of the beam quality product. Hence this embodiment is particularly suitable for focussing the light emitted by a multimode laser diode onto an optical fiber.
According to a preferred embodiment of the present invention the device is provided as a substantially cuboid body, having one entry plane and one exit plane which are parallel to each other and the distance between which preferably corresponds to twice the focal length of the segments of cylindrical lens. The parallel arrangement of entry and exit plane assures that beams of light maintain their direction after their passage through the device. Choosing the distance between entry and exit plane to be equal to twice the focal length of the segments of cylindrical lens ensures that beams of light undergo only rotation but not focussing or expansion when passing through the device.
According to an alternative preferred embodiment of the present invention the device consists of two substantially cuboid bodies, each of which comprises an entry plane and an exit plane parallel to said entry plane, the distance between the two planes preferably being smaller than the single focal length of the segments of cylindrical lens. These two cuboid bodies are preferably arranged with respect to each other in such a way, that the cylindrical lenses, formed by segments of cylindrical lens facing each other in each one of the two bodies, have a common focal plane between the cuboid bodies. One effect of this arrangement is to ensure that beams of light passing through the device will undergo only rotation and not focussing or expansion. Moreover, due to focussing of beams of light passing through the device into the common focal plane between the cuboid bodies, light sources with a greater divergence in one direction or light sources with emitting sections positioned close to each other in one direction can be handled more effectively as well, allowing a reduction of losses in imaging, for example onto the front face of an optical fiber.